Such a flight control indicator is more specifically adapted to an airplane, in particular a military transport airplane, which is generally very heavy and whose maneuvering times are relatively long.
Although not exclusively, the present invention applies more particularly to low-altitude flight. The expression low-altitude flight is intended to mean flight along a flight trajectory (at low altitude) allowing an aircraft to follow as closely as possibly the terrain over flown, in particular to avoid being pinpointed. A low-altitude flight trajectory such as this is therefore situated at a terrain height which is generally less than a predetermined height, for example 500 feet (around 150 meters).
A low-altitude flight trajectory such as this may comprise rectilinear climb and descent segments. This flight trajectory is computed, taking account in particular:                of a speed preset selected by the crew;        of the predicted weight of the aircraft over the trajectory;        of the maximum climb and descent capabilities of the aircraft (given by a standard model of performance); and        of a given thrust, for example the maximum continuous thrust MCT for the climb preset and the idle (or idling thrust) for the descent preset.        
In this case, if the computed slope of the flight trajectory is not correct, that is to say if it is larger than the maximum slope able to be reached (in particular on account of a model of performance of the aircraft which is too optimistic, of meteorological conditions which have not been taken into account correctly, or of an error in the computation of the maximum climb slope), when the aircraft is controlled by an automatic thrust control system (“auto-thrust” system), the thrust is increased in such a way as to reach and maintain the requested slope, while retaining the selected speed preset. The thrust may then increase until it reaches the limit value of maximum thrust of said automatic thrust control system. When this limit value is reached, the speed begins to drop, and this may of course lead to a very dangerous situation, especially when the speed of the aircraft on dropping approaches the stalling speed. Moreover, in general, the throttle does not move through the gate, when the thrust is adjusted automatically in this way.
Consequently, the pilot of the aircraft is not furnished with sufficient information regarding in particular the thrust engendered, in such a situation which is liable to be very dangerous, as indicated hereinabove.